During the fabrication of large scale laminate structures, a group of plies arranged as a kit may be sequentially laid up at particular locations on a tool in order to strengthen, stiffen or otherwise provide a structure with desired structural or performance characteristics. The use of a ply kit may be efficient in some applications since it frees automated tape laying equipment from laying up many relatively small plies in localized areas. Ply kits may be used, for example and without limitation, where it is desirable to fill gaps between stringers and frames of an airframe using a composite filler. The filler comprises a set of laminated filler plies that are sequentially placed on a tool before full plies are laid up over the filler. The filler plies may be placed within pockets in the tool that are specially shaped and located to form a shaped filler when the pocket is filled with plies. In the past, the layup process was performed by hand.
Hand layup techniques may be required in other applications. For example, it may be necessary to layup plies, such as doublers in precise locations on a substrate relative to each other. Using hand layup techniques, the technician must place each individual ply on the substrate at a precise location relative to other plies. Moreover, the hand layup technique requires placement of plies one-at-a-time, and the size of the plies is limited to that which the technician can manually handle. In other applications, hand layup may be necessary where the ply material is relatively delicate and/or subject to wrinkling, creasing or tearing when processed by AFP machines. For example, protection of aircraft against lightning strikes may be achieved by applying a grid of thin copper foil-sheets to exterior skins of the aircraft. The grids are assembled by one-at-a-time by hand layup of hundreds of pieces of relatively small thin copper foil sheets that may be subject to wrinkling, denting, creasing and/or tearing during the layup process.
The hand layup techniques described above are time consuming, labor intensive and may not be well suited to higher production environments. Accordingly, there is a need for an automated layup system that reduces hand labor and layup time, and provides reliable precise placement of material plies on a substrate such as a tool. There is also a need for a layup process that allows placement of larger plies in order to reduce the total number plies that need to be laid up to form a structure.